There exist a number of methods for averting the conflict of requests to use hardware resources (simply called resources hereunder) from a plurality of executing tasks. Illustratively, one method (called the first method hereunder) involves limiting the right to use resources according to predetermined priority. Another method (the second method) is a so-called single task method that limits the number of executable applications to a single task at any one time. A further method (the third method) involves allowing only the first application that has acquired a resource to utilize those resources at any one time. An even further method (the fourth method) involves implementing by software a layer in which hardware resources are represented by abstract entities so that the resources may be accessed simultaneously on a virtual basis.
Japanese Patent Laid-open No. Hei 9-16416 (FIG. 1) discloses a technique for allocating hardware resources. The disclosed technique involves adjusting, in a multitask processing environment, the waiting times of processing requests for resources depending on the degree of congestion of the requests so that the resources may be allocated preferentially. In other words, processing requests of lower priorities are delayed variably depending on the degree of their congestion so that the resources are allocated preferentially for requests of higher priorities.
However, the first and the second methods above have the disadvantage of entailing restrictions on the performance of applications; a method involving fewer operational constraints is preferred. The third method requires that resource requests have the same priority within the system; any differences that may exist in priority are ignored. If it is desired to allocate resources according to priority by the third method, it is necessary to carry out priority management on the user's responsibility. For the fourth method, a high-performance environment such as a personal computer is mandatory; the scheme involved is too burdensome for devices with limited functions and capabilities such as mobile phones.